The federal government shut down at the stroke of midnight Friday, halting all but the most essential operations, after Republicans and Democrats were unable to agree on a compromise.

Here are some things you should know about the shutdown and its impact on daily life:

Mail Delivery: Post offices will remain open, and mail will be delivered

Social Security: Benefits checks will continue to be mailed out

Airports: Airports will remain open, and air traffic controllers and TSA workers will remain on the job

Passports: Passport agencies will remain open, but passport applications could be delayed

National Parks: Parks -- including the Statue of Liberty and Ellis Island -- are closed, although the Interior Department says it will work to keep public lands "as accessible as possible"

Museums: The Cooper Hewitt design museum and Heye Center in New York City are closed

Military: Active duty military personnel will continue to work, while non-essential civilian Department of Defense employees would be furloughed. Military members get paid on the 1st and 15th, so if a shutdown continued through February 1, U.S. troops would not get paid

The entire federal government doesn't shut down

In 1981, the Office of Management and Budget identified three "excepted activities" that will continue regardless of a shutdown: those "authorized by law," those that "protect life and property" and those "necessary to begin phasing out of other activities."

Government functions relating to emergency and disaster assistance, criminal investigations, air traffic control, protection of federal property and other activities "essential to ensure continued public health and safety" - like food inspections and hazmat management - continue to operate, although usually with a reduced workforce.

Of the more than 2 million civilian employees of the federal government, approximately 850,000 were furloughed at the peak of the 2013 government shutdown.

Shutdowns cost the government money

Lost productivity cost the federal government $2 billion in payroll alone during the 2013 shutdown, according to the Office of Management and Budget. The office also noted that the federal government was unable to collect certain fees and had to pay additional interest on payments made late due to the shutdown.

Similarly, the 1995-1996 shutdowns are estimated to have cost the federal government approximately $2.1 billion when adjusted for inflation, according to the Pew Research Center, much of which was in back pay to furloughed workers.

Shutdowns don't just impact government employees

The 16-day government shutdown in 2013 had far-ranging impacts. Each day, an estimated 700,000 people were unable to visit shuttered national parks and destinations like the National Zoo, costing the economy more than $75 million daily. So-called "death benefit" payments to families of deceased service members were delayed, and processing of things like federal loan and permit applications were put on hold.

Polling shows that voters generally oppose the prospect of a government shutdown, and shutdowns that do happen can damage Americans' view of government as a whole. According to Gallup, "People want their elected representatives to compromise rather than stick to principle and get nothing done."

During the 2013 shutdown, Gallup said, Americans supported a compromise 2-1, and many were more likely to "say the shutdown was an attempt by both sides to gain political advantage than to say it was an important battle over principles and the future direction of the government."

An ABC News-Washington Poll found that 78 percent of Americans viewed the 1995-1996 shutdown as a bad thing.

The longest shutdown was three weeks

In the final days of 1995, large portions of the federal government shut down for three weeks following a dispute between President Clinton and Republicans. It followed another six-day shutdown just a month prior.